It is known, as for example from German patent document No. 2,919,105 filed by R. Verbickas et al with a claim to the priority of U.S. application Ser. No. 907,502 filed May 19, 1978, now abandoned, and from U.S. Pat. Nos. 2,776,586 and 3,857,268, to use working rolls of noncylindrical shape in a roll stand, and to provide means for displacing at least one of these rolls axially relative to the other and for bending at least one of these rolls. In this manner it is possible to change the dimension of the gap or so-called nip formed between the two rolls.
The disadvantage of such a system is that the provision of the bending equipment for the roll adds considerably to the cost of the rolling stand. On the one hand it is necessary to provide roll-bending devices that bend the ends of the roll away from the nip, so-called positive bending, and separate equipment for bending of the ends of the roll toward the nip, so-called negative bending. Positive bending increases the pressure at the longitudinal edges of a workpiece being rolled and negative bending decreases this pressure, for corresponding decreases and increases in workpiece thickness at these edges.
It is possible to achieve only minimal variations in nip dimensions without this bending equipment. That is, without using the bending equipment it is impossible to achieve anything other than slight variations in a workpiece with longitudinal edges thicker than its middle.
Not only is this type of arrangement quite expensive, but accurately establishing the proper amount of bend in conjuction with the right axial position of the working roll is very difficult, requiring expert setup personnel and frequent monitoring during operation to verify that the system remains properly set up. What is more, when positive bending is employed it is necessary to exert enormous forces against the working-roll ends, so that the roll-stand housing must be overdimensioned considerably.